Brush construction for a small electrodynamic machine

ABSTRACT

A brush-holder assembly for an electrodynamic machine such as an electric motor, with the brush-holder arm urged by a separate leaf spring both axially and laterally.

[ 1 Jan.30,1973

United States Patent [191 Dijkstra [54] BRUSH CONSTRUCTION FOR A [56]References Cited [TED STATES PATENTS SMALL ELECTRODYNAMIC MACHINE [75]Inventor:

Homme Dijkstra, Drachten, Netherlands Schultz................ Van Dijket al. Mabuchi lll] Edmundson.....

[73] Assignee: Philips Corporation, New

York,N.Y.

22 Filed: Mayl1,l97l 21 Appl.No.: 142,398

FOREIGN PATENTS OR APPLICATIONS Related US. Application DataContinuation of Ser. No. 864,380, Oct. 7, I969,

v abandoned.

8/l966 Great Britain.......................310/239 Primary Examiner-D.F. Duggan Att0rneyFrank R. Trlfari ABSTRACT [30] Foreign ApplicationPriority Data PAIENIED'JAHO I975 3,714,481

INVENTOR.

HOMME DIJKSTRA BY A ENT

one end presses against a rigid point of support of the machine and withits other end resiliently loads the brush-holder arm.

Such a brush construction is known from British Patent Specificationl.0l0,244, in which two brushholder arms are arranged one on each sideof a commutator in an end shield, each brush holder arm being at a pointintermediate the brush and one end of the brushholder arm by a bent leafspring arranged in the respective end shield, one end of eachbrush-holder arm pressing pivotably, by means of an arcuateportion,against a pivot pin rigidly secured to the end shield. The forceexerted on the commutator by the brush depends on several factors, suchas the manufacturing tolerances in the dimensions of the leaf spring andin its location in the end shield, the tolerances with respect to thepoint at which the leaf spring exerts pressure on the brush-holder armand finally the angular position occupied by the brush-holder arm, inview of the spring characteristic of the leaf spring. The latter angularposition is itself dependent on several manufacturing tolerances in thedimensions and disposition of various component parts and in additiondepends on the degree ofwear of the brush.

It is an object of the invention to provide a brush construction of theabove-mentioned kind in which the brush pressure is less dependent uponmanufacturing tolerances and upon brush wear, and the invention ischaracterized in that the said resilient load is mainly due to bucklingof the leaf spring. While retaining the leaf spring, which is attractivefor use in small electrodynamic machines, because of its simplicity andcheapness, the arrangement according to the invention provides a springcharacteristic within a comparatively wide range and a brush pressurewhich only slightly depends on manufacturing and assembling tolerances.

An embodiment of the invention is characterized in that the pivotableattachement comprises a knife-edge bearing and that the leaf springexerts a force on the brush-holder arm acting in the direction from theknife edge to the supporting surface of the knife-edge bearing. Thispermits a very simple bearing construction.

A further embodiment of the invention is characterized in that thebrush-holder arm is brought out through an aperture provided in themachine and in that the part thus protruding from the machine isextended so as to be capable of being pivoted by hand. This embodimentis of particular importance for the assembly and for the prevention ofdamage to the frequently small and hence vulnerable brush constructionswhich are used in the small electrodynamic machines to which theinvention relates.

A still further embodiment of the invention for use in combination withone of the two last-mentioned embodiments is characterized in that thebearing surface of the knife-edge bearing and the brush rocker of themachine are an integral unit made of a synthetic material. In such anembodiment the entire brush construction may be mounted on the saidbrush rocker and only at a later stage of the assembly, the brush rockerwith the brush construction mounted on it is mounted in the machine asan integral unit.

The invention will be described more fully with reference to theaccompanying drawing, the single FIGURE of which shows an embodiment ofthe invention.

in the Figure, pivotably secured brush-holderarms 1 form part of a brushconstruction of a small direct-voltage commutator motor for use in anelectric dry-shaving apparatus. The brush-holder arms I carry gauzebrushes 2 which are pressed against the commutator 3 of the motor. Eachof two leaf springs 4, pressed with one end against a fixed support 5 ofthe motor at reference point 14, and with its other end against one ofthe brush-holder arms 1 at reference point 15, so

that these arms are resiliently loaded. The two leaf springs 4 in theirunmounted condition are flat having an initial length L defined by astraight line between the ends of the spring and during assembly aregiven the buckled shape shown in the drawing whereby the spring has aloaded length L defined by a straight line between the ends of thespring, L being obvioisly less than L So that the resilient loading ofthe brushholder arms 1 is mainly due to the buckling or column loadingof the leaf springs, for owing to their elastic properties these springstend to stretch to regain their flat state. As is obvious from thedrawing, the length L of the buckled spring is the same as the distancebetween reference pointsl4 and 15 established by the frame and thearm 1. It thus follows, that this distance L is less than the initial,unloaded length L of the spring.

The pivotable attachment consists of a knife-edge bearing, and to theleaf springs 4 exert a force on the brush-holder arms which acts in thedirection from the knife edge to the bearing surface of the knife-edgebearing. The resilient load imposed on the brush-holder arms 1 by theleaf-springs 4 thus serves-a double pur pose, namely firstly resilientlypressing the gauze brushes 2 to the commutator, and secondly thrustingand fixing the knife edge in the bearing recess which is the supportingsurface of the knife-edge bearing.

The brush-holder arms 1 are brought out through a slit-shaped aperture 6and the part protruding from the machine is extended so as to enable itto be pivoted by hand. By pressing the two ends 7 together between thumband first finger, the brush-holder arms can readily be lifted from thecommutator, simplifying assembly and protecting the comparativelyvulnerable and small brush-constructions during assembly.

The bearing surface of the knife-edge bearing is integral with aplastics brush rocker 8 of the motor and forms part of the upper surfaceof the said brush rocker on either side of the slit-shaped aperture 6,in conjunction with a number of bosses 9. The brush-rocker 8 maypreviously be provided with the complete brush construction and at alater stage of the assembly may be secured to the end shield 11 of themotor by, means of tapping screws 10. Current is supplied to the brushesconsecutively through soldering lugs 12 located under the tapping screws10, short lengths of stranded wire 13 connected to the brush-holder arms1 by spot-welding, brush-holder arms 1 and gauze brushes 2.

What is claimed is:

1. In an electrodynamic machine including a frame having aspring-engaging first reference point, an assembly for holding a brushagainst a commutator, the assembly comprising at least one arm having afirst end part pivotally secured to the frame, a remote part holding thebrush, and a second reference point along the length of said arm, theassembly further comprising a leaf spring which is generally flat in itsunloaded condition defining an initial length between its ends, thisspring when assembled being bowed under a buckling load whereby thespring has a first end secured to the frame at said first referencepoint and the spring has a remote part engaging the arm at said secondreference point, the distance between said two points being less thansaid initial spring length, the spring so loaded exerting a force on thearm both axially along the length thereof and laterally relative to saidpivot and thereby resiliently positioning and urging the brush againstthe commutator, said spring having a spring characteristic which is verylevel within a comparatively wide range of spring deflection.

2 Apparatus according to claim 1 wherein the frame defines an aperturethrough which the first part of the arm extends externally, whereby saidfirst end is manually removable from the frame.

3. In an electric motor including a frame having a spring-engaging firstreference point, and commutator and brush elements, the improvement incombination therewith of an assembly for holding each brush against thecommutator, comprising for each brush an arm having a first end-partpivotally secured to the frame, a remote part holding the brush, and asecond reference point along the length of said arm, and-a leaf springwhich is generally flat in its unloaded condition defining an initiallength between its ends, this spring when the spring has a first endsecured to the frame at said first reference point and the spring has aremote part engaging the arm at said second reference point, thedistance between said two points being less than said initial springlength, the spring exerting a force on the arm both axially along thelength thereof and laterally relative to said pivot and therebyresiliently positioning and urging the brush against the commutator,said spring having a spring characteristic which is very level within acomparatively wide range of spring deflection.

4. Apparatus according to claim 3 wherein said spring has a springcharacteristic which is very level within a comparatively wide range ofspring deflection.

5. Apparatus according to claim 3 wherein said pivoted engagement ofsaid first end part comprises a knife-edge bearing.

6. Apparatus according to claim 3 wherein the frame defines an aperturethrough which the first part of the arm extends externally, whereby saidfirst end is manually removable from the frame.

7. In an electric motor including a frame, a commutator rotatable aboutits axis, and at least two separate brushes engaging the commutator, theimprovement in combination therewith of an assembly for positioning eachbrush comprising an arm having a first end secured to the frame andpivotable about an axis generally parallel to the commutator axis, and asecond part remote from the first part and to which the brush issecured, a leaf spring having a first end engaged to the frame and asecond end which is remote from the first end and engages the arm, thespring being flexed m columnar loading whereby the spring resilientlyurges assembled being bowed under a buckling load whereby the armaxially along its length and laterally relative to its pivot point andthe brush is resiliently urged against the commutator. v

1. In an electrodynamic machine including a frame having aspring-engaging first reference point, an assembly for holding a brushagainst a commutator, the assembly comprising at least one arm having afirst end part pivotally secured to the frame, a remote part holding thebrush, and a second reference point along the length of said arm, theassembly further comPrising a leaf spring which is generally flat in itsunloaded condition defining an initial length between its ends, thisspring when assembled being bowed under a buckling load whereby thespring has a first end secured to the frame at said first referencepoint and the spring has a remote part engaging the arm at said secondreference point, the distance between said two points being less thansaid initial spring length, the spring so loaded exerting a force on thearm both axially along the length thereof and laterally relative to saidpivot and thereby resiliently positioning and urging the brush againstthe commutator, said spring having a spring characteristic which is verylevel within a comparatively wide range of spring deflection.
 1. In anelectrodynamic machine including a frame having a spring-engaging firstreference point, an assembly for holding a brush against a commutator,the assembly comprising at least one arm having a first end partpivotally secured to the frame, a remote part holding the brush, and asecond reference point along the length of said arm, the assemblyfurther comPrising a leaf spring which is generally flat in its unloadedcondition defining an initial length between its ends, this spring whenassembled being bowed under a buckling load whereby the spring has afirst end secured to the frame at said first reference point and thespring has a remote part engaging the arm at said second referencepoint, the distance between said two points being less than said initialspring length, the spring so loaded exerting a force on the arm bothaxially along the length thereof and laterally relative to said pivotand thereby resiliently positioning and urging the brush against thecommutator, said spring having a spring characteristic which is verylevel within a comparatively wide range of spring deflection. 2.Apparatus according to claim 1 wherein the frame defines an aperturethrough which the first part of the arm extends externally, whereby saidfirst end is manually removable from the frame.
 3. In an electric motorincluding a frame having a spring-engaging first reference point, andcommutator and brush elements, the improvement in combination therewithof an assembly for holding each brush against the commutator, comprisingfor each brush an arm having a first end-part pivotally secured to theframe, a remote part holding the brush, and a second reference pointalong the length of said arm, and a leaf spring which is generally flatin its unloaded condition defining an initial length between its ends,this spring when assembled being bowed under a buckling load whereby thespring has a first end secured to the frame at said first referencepoint and the spring has a remote part engaging the arm at said secondreference point, the distance between said two points being less thansaid initial spring length, the spring exerting a force on the arm bothaxially along the length thereof and laterally relative to said pivotand thereby resiliently positioning and urging the brush against thecommutator, said spring having a spring characteristic which is verylevel within a comparatively wide range of spring deflection. 4.Apparatus according to claim 3 wherein said spring has a springcharacteristic which is very level within a comparatively wide range ofspring deflection.
 5. Apparatus according to claim 3 wherein saidpivoted engagement of said first end part comprises a knife-edgebearing.
 6. Apparatus according to claim 3 wherein the frame defines anaperture through which the first part of the arm extends externally,whereby said first end is manually removable from the frame.